1. Field of the Invention
This invention relates to a method for mixing a plurality of gases efficiently and an apparatus therefor.
2. Description of the Related Art
As means to mix a plurality of gases, the apparatus described in GB 2061744 A and static mixers are known. They are invariably complicated in construction because they have internal items disposed therein, they give rise to pressure drop during the service, and possibly fail to offer expected services when the gases to be mixed contain an adhesive substance and/or a solid matter.
JP-A-10-244,136 discloses an apparatus which has gas inlet orifices so set that their diameters equal the rates of inflow of the relevant gases to a mixing device. The single mixing device, however, is incapable of adjusting the mixing ratio of the gases being introduced therein.
The method for mixing a plurality of gases is particularly important when the raw materials are mixed for the reaction of catalytic gas phase oxidation. In the reaction of catalytic gas phase oxidation, an organic compound or a gas containing an organic compound is mixed with a gas containing a molecular oxygen. As concrete examples of the reaction of catalytic gas phase oxidation contemplated herein, it may be cited, for example, ethylene oxide from ethylene, maleic anhydride from benzene or C4 hydrocarbon, phthalic anhydride from xylene or naphthalene, acrolein from propylene or propane, acrylic acid from acrolein, methacrolein from isobutylene or tertial butyl alcohol, and methacrylic acid from methcrolein.
FIG. 1 is an explanatory diagram illustrating one example of the conventional gas mixing apparatus. A gas mixing apparatus 1, illustrated in FIG. 1, is a vessel 5 provided, on the lateral face thereof, with a first gas inlet nozzle 2 and a second gas inlet nozzle 3 and in the upper part thereof with a gas outlet 4. This vessel 5 measures 600 mm in diameter and 2850 mm in length (though the length is not easily specified on account of the use of pipes, it is safe to fix the length at the magnitude mentioned above because the required mixture was believed to be completed till the component gases reach the sampling nozzle).
The first gas inlet nozzle 2 measures 550 mm in diameter and the central part of the first gas inlet nozzle 2 is disposed at a position of 550 mm from the bottom of the vessel 5. The second gas inlet nozzle 3 measures 80 mm in diameter and the central part of this second gas inlet nozzle 3 is disposed at a position of 1000 mm from the bottom of the vessel 5. These nozzles are laid as opposed to each other in the direction from the exterior to the interior of the vessel 5.
FIG. 2 is an explanatory diagram illustrating the conventional gas mixing apparatus shown in FIG. 1 as viewed from the gas outlet side (the sampling nozzle is not shown) . In the gas mixing apparatus 21 illustrated in FIG. 2, the gases to be mixed are introduced into the vessel 25 via the first gas inlet 22 and the second gas inlet 23, mixed in the vessel 25, and discharged as a mixture via the gas outlet 24.
Generally, the mixing ratio of these gase is decided so as to prevent the mixture from falling within the explosion limits. The substances handled during the course of mixing, depending on their kinds, have an inevitable possibility that they will locally and momentarily form a composition falling in the explosion limits.
For the purpose of mixing gases rapidly as well as simplifyng the construction and avoiding the pressure drop to the fullest possible extent, expediting the mixture lest the gases within the explosion limits should grow in volume, and increasing the yield when the apparatus is used for the production of organic compounds, the mixed gas is required to homogenize at the entry to the reactor for catalytic gas phase oxidation.
It is an object of this invention to provide a method for mixing a plurality of gases different in kind which incurs pressure drop only in a substantially negligible degree and allows application even to gases containing adhesive substances and/or solid matter, and an apparatus for use in the method.
In mixing a plurality of gases which are capable of forming a composition falling in the explosion limits, the mixed gas of a composition within the explosion limits which is locally formed during the course of mixing is required to reduce in volume by expediting the mixture.
The object of this invention is achieved by a method for mixing a plurality of gases which is characterized by forming a helical flow within a mixing vessel.
The object of this invention is also achieved by an apparatus for mixing a plurality of gases, characterized by having at least one gas inlet nozzle or gas outlet nozzle so disposed as to form a helical flow within a mixing vessel.
According to the apparatus of this invention for mixing gases, since the internal items of the mixing vessel are substantially eliminated or decreased to the fullest possible extent, the gases can be homogeneously mixed with an apparatus exceptionally simple in construction.
According to the method of this invention for mixing gases, the gases can be mixed homogeneously and conveniently.